photo of a water operator flushing a fire hydrant with the heading Hydrant Flushing.

Hydrant Flushing FAQs

What is Hydrant Flushing?

Hydrant flushing is a release of water from fire hydrants. It is a controlled procedure that is vital to the general maintenance of Sun Prairie’s water distribution system.

Why do Utilities flush hydrants? 

Often Utilities flush to improve water clarity, appearance, and quality by clearing settled iron and other minerals from the water mains (distribution pipes.) By flushing a lot of water through the pipes, these settled minerals are stirred up and are flushed out of the mains. Iron and other minerals can temporarily look like tea-colored water coming out of a hydrant, the water is still safe to drink and use, however it may stain laundry. 

Hydrant flushing helps avoid random occurrences of rusty water if there is a large demand for water, such as during a major firefighting effort. Water mains are also flushed to physically operate the hydrant (called “exercising”) and to inspect for hydrant maintenance needs.

How often do Utilities flush the mains? 

Some utilities flush quite often, as much as monthly due to high mineral content, stagnant water, or other reasons. Fortunately, Sun Prairie does not have many iron or mineral issues. Sun Prairie Utilities flushes hydrants at least every other year as required by Wisconsin State code NR 810.13. In areas where water may move more slowly through the system, such as hydrants located on a dead-end main, hydrants are flushed twice annually to maintain water quality.

Primarily Sun Prairie Utilities flushes to operate and inspect each hydrant to ensure proper performance when needed and to replace damaged hydrants.

How long does it take to flush, and is there a schedule when crews will be in my area?

Sun Prairie has approximately 1,800 hydrants to flush and it takes quite a while to operate and inspect each hydrant. Typically flushing takes place April through October each year. Flushing is worked into the crew schedule based on weather, staffing levels, and other scheduled work so it is difficult to provide a schedule with specific dates or times.

My water is discolored, what do I do? 

Sometimes, as the churned-up water passes by your water service on the way to the hydrant, some discolored water may go up into the service line leading to your house, especially if you have a faucet on or an appliance is drawing water. If your water is discolored, wait until flushing on your street has subsided and then run a garden hose for five minutes or run a cold-water tap for 10 minutes, until the water runs clear.

If flushing is taking place, do not open the faucet or use water until the flushing is completed on your street.  If you are not home and appliances are not running at the time of flushing, it’s unlikely that you will draw in any discolored water. 

If you have a water softener and are experiencing discolored water, place the unit into “regeneration or cleaning mode” after hydrant flushing is completed in your area.

Is the water safe to drink while flushing?

Yes, discolored water is safe to drink and use, however it may stain laundry.

While low concentrations of minerals are harmless, they can discolor the water causing users concern about the water quality and/or stain clothes in the laundry machine. Sun Prairie’s low iron means there is not much iron to flush out, but caution should still be exercised when running loads of laundry.

My laundry is stained, what do I do now?

Keep the laundry wet and use an iron or stain-removing product like “Iron Out” rust and stain remover.

What if I have other questions? 

For more information, contact Sun Prairie Utilities at or (608) 837-5500.